If coryneform bacteria are cultured in a medium containing a restricted amount of biotin, the bacteria produce a marked amount of L-glutamic acid. On the other hand, if coryneform bacteria are cultured in a medium containing an excessive amount of biotin, the bacteria do not produce L-glutamic acid. However, it is known that, even under such a condition, if a surface active agent or a biotin activity suppressor such as penicillin is added to the medium, growth of the bacteria is suppressed and they become to produce a marked amount of L-glutamic acid.
The glutamic acid production induced by addition of penicillin to a medium has been studied for many years (T. D. Nunheimer, J. Birnbaum, E. D. Ihnen and A. L. Demasin, Appl. Microbiol., 20, 215–217 (1970)). The effect of penicillin is considered to cause structural change of cellular surface layers, thereby enhancing permeability of cytoplasmic membranes for glutamic acid.
In addition, it has also been studied through what kind of mechanism the restriction of the biotin amount or the addition of a surface active agent or penicillin influences the productivity of L-glutamic acid of coryneform bacteria, and presence of a gene considered to participate in the L-glutamic acid production has been elucidated (dtsR gene). Further, it has been confirmed that a strain of which dtsR gene is disrupted produces a marked amount of L-glutamic acid even under a condition in which biotin is present in such an amount that a wild strain hardly produces L-glutamic acid (International Patent Publication WO95/23224).
Furthermore, there have been obtained many findings that contradicts the explanation that the glutamic acid production is induced the enhancement of permeability of cytoplasmic membranes, and the mechanism of the glutamic acid production induced by penicillin has still been unknown (E. Kimura, Y. Kawahara and W. Nakamatsu, Tanpakusshitu Kakusan Koso (Protein, Nucleic acid and Enzyme), vol. 42, pp. 2633–2640 (1997)).
By the way, it is well known that penicillin binding proteins (PBPs) play an important role in bacterial cell division. The penicillin binding proteins are considered to be enzymes that exist in bacterial cellular surface layers, and they specifically bind to β-lactam antibiotics such as penicillin. Although it may vary depending on the species, it is considered that 3–8 kinds of the proteins are usually found in Escherichia coli, and their molecular weights are distributed around the range of 40,000–120,000. Penicillin inhibits the enzymatic reactions by binding to a serine residue of an active site of the penicillin binding proteins.
It has been elucidated that 7 kinds of penicillin binding proteins exist in Escherichia coli (E. coli), which was especially a main target of researches (B. G. Spratt, Proc. Natl. Acad. Sci. U.S.A., 72, 2999 (1975)). Among those, those designated as PBP2 and PBP3 have been demonstrated to play an important role in cell division (B. G. Spratt, J. Bacteriol., 131, 293 (1977)). However, it has not been known whether penicillin binding proteins exists in coryneform bacteria.